Method of coating ferrous metals with magnesium and magnesiumbase alloys



Patented May 1, 1951 ES PATENT OFFICE UNITED STAT METHOD OF COATING FERROUS METALS WITH MAGNESIUM AND MAGNESIUM- BASE ALLOYS No Drawing. Application May 2, 1947, Serial No. 745,636

The invention relates to a method of coating iron and steel with magnesium and magnesiumbase alloys. improved method of applying a coating of mag:-

It more particularly concerns an- 3 Claims. (Cl. 117-52) of each such chloride are to be preferred. The presence of other alkali metal chlorides in the flux may be tolerated, as for example lithium chloride, in minor amount but its use is usually nesium or magnesium-base alloy froma molten 6 nec nomic. bath of such metal to the surface of an article The coatin metal may be melted in any suitof. iron or steel. t t t able melting vessel, such as an iron or steel cru- ,,The p c pal Object of h inven n s p cible, under the protection of a quantit of the vide articles of iron and steel with an adherent flux of th aforesaid composition. The flux is coating of magnesium an 3 thereof in 10 lighter than the molten metal and largely floats \Vhich magnesium is the predominant constituent. on u per urface Usually enough flux Other objects and advantages will appear as the used to make a layer about an inch deep over the description of the invention proceeds. pool of molten coating metal in the crucible, al-

fiy, the method fio'rltemplated y the though other amounts of flux may be used. vention comprises first fluxing the clean article The coating m t p00] and flu t is main; to bflcoated and then mil-musing the fiuxed tained at a temperature in the range of about; time n o a p001 of a molten coating metal of 725 to 925 0. depending upon the melting point magnesium 0 a magnesium-base 51-110379 The i of the coating metal. Temperatures slightly ticlebecomes wetted by the coating metal which above the melting point of the Coating metal are t fl dlsplaces the the ff The preferred. In most instances, a temperature in liquid ,metal Wetted article is then Withdrawn the range of to C is Satisfactory pool of P metal and sowed so as The iron or steel article to be coated is int1'o- 9 h W Coating duced into the flux layer so as to flux the coated In car-mag method the ,surface of the article before contact with the liquid coating mm or fteel artcle 1f F already metal. Contact with the coating metal results f ajllylfree froin t fi t clearelled in displacement of the flux from the surface of ig g f gfigg gigg ii g i gii g g g the article and the coating thereof with liquid and may be accomplished imme rsion in a 15 s i g f left in a me a p00 a ew mlnu es e ore elng remove used from the coating metal pool lhfOllgh the flux into In order torender the cleaned surface of the the atmosphere and suxigsequemly 9 9 iron or steel wettable by molten magnesium and 11:18 temptmwre, i which magneaum and its alloys, we have compounded certain saline alloys mpldly 03101128 Above the flux we fluxes that can be used as fluxing agents AS provide an ambient amosphcre of argon, helium, compounded, they have the property of both proi f it fs i g ii j tecting the molten 01 of coating metal from ar 16 6 rom con ac h 19 oxidation and render i g the iron or steel wettable air until enqugh to solidijfy the coatingby the coating metal. Among the suitable fluxes Thereafter, the artlcle may be qulckly Cooled and are those which comprise mixtures of alkali chlow l freed from adhering flux as 10y quenchrides, preferably sodium and potassium chlomg In Water ride, to Which is added between about 1 and 20 g n q us a given b li c l l se s per cent of magnesium fluoride (MgFz), a1- 0011 amma W1 magneslum c 0Y1 e W 19; though preferred proportions are between about gradually tsh tf due to the aritiontof the mac- 3 and 6 per cent. If more than about 6 per cent nesillm in 8 e me all p on e flu A5 of magnesium fluoride is used, it separates from the flux becomes excessively contaminated with th balan e of the flux as 6 per cent is about magnesium chloride its effectiveness to bring the limit of its solubility. Barium fluoride may about wetting of iron or steel b molten magbe used similarly. 'Various proportions of sodium nesium and its alloys is destroyed. We have and potassium chloride may be used, such as found that the maximum amount of magnesium those in the range of 20 parts of sodium chloride chloride that can be tolerated in the flux comand parts of potassium chloride to 80 parts position in about 5 per cent by weight. Best reof sodium chloride and 20 parts of potassium sults are had when the flux contains about 1 to chloride, although approximately equal amounts as 2 per cent of magnesium chloride as this salt tends to reduce the oxidation of the coated article as it is withdrawn from the flux layer.

Example The following example is illustrative of the invention:

Test pieces of mild steel 1" x 2" x which were cleaned of foreign material by pickling in a 25 per cent HCl at 150 F. for 15 minutes followed by a further pickling for 15 minutes in a non aqueous solution comprising ethyl alcohol saturated with HCl gas, the solution thus saturated containing 0.4 gram of HCl per gram of ethyl alcohol, were coated in accordance with the invention. The clean test pieces were introduced into a molten salt flux bath overlaying a pool of molten magnesium. The flux was composed of per cent of K01, 42 per cent of NaCl, and 5 per cent of MgFz, the temperature of the flux and metal was between about 750 and 800 C. pieces thus fluXed were passed from the flux directly into the molten metal. The test pieces were thus first wetted by the molten flux and then by the molten magnesium which displaced the flux from the surface of the test pieces thereby coating them with magnesium. The magnesium coated test pieces were left in the pool of molten magnesium for about 3 minutes. All atmosphere of argon was provided over the flux bath and the coated test pieces withdrawn from the bath into the argon atmosphere where they were allowed to cool below about 500 C. The so-called test pieces were then quickly transferred to a water bath which quenched the test pieces to room temperature and washed off adhering flux. Examination showed that each piece was uniformly coated with a continuous adherent layer of magnesium in crystalline form having a thickness of about 0.001 inch.

Similar operations with magnesium-base alloys such as those containing aluminum, zinc or both with or without manganese, as in the usual commercial magnesium-base alloys, produced similar coatings on iron and steel articles, the crystals of the coating metal being finer in the case of magnesium-base alloys than those obtained with unalloyed magnesium.

The effectiveness of the coatings to protect steel from atmospheric corrosion has been ascertained by providing steel test panels with a coating as described 0.001 inch thick of a magnesiumbase alloy having a nominal composition of 6.0 per cent of aluminum, 0.2 per cent of manganese, 3.0 per cent of zinc, the balance being magnesium,

and subjecting the so-coated panels to atmos- I pheric exposure. For comparison, similar test panels were coated with zinc 0.001 inch thick and subjected to the same atmospheric exposure conditions. After about two months of such continuous atmospheric exposure the Zinc coated steel panels were largely denuded of the zinc coating and the denuded area covered with rust While the The test 4 coating of the magnesium-base alloy coated steel panels was still intact and the panels substantially free from rust.

Among the advantages of the invention are that thin uniform adherent coating of magnesium and its alloys may be provided upon iron or steel articles. The coatings serve to protect iron or steel from atmospheric corrosion. The coating makes possible bonding magnesium or alloy thereof to an iron or steel article as by casting magnesium or a magnesium alloy in direct contact therewith when provided with the coating as described. The coating in such applications acts to promote good adhesion of the article to the cast metal. Attempts to pull apart an iron or steel article and a magnesium or magnesium alloy article cast against the iron or steel article coated according to the method described requires the application of a tensile stress almost equal to the ultimate strength of the metals involved.

- We claim:

1. The method of producing an adherent coating of a coating metal of the group consisting of magnesium and magnesium alloys upon articles of ferrous metal which comprises introducing the article to be coated into a molten body of the coating metal through a flux layer floating upon said molten body of coating metal, the flux consisting of a mixture of 20 to 80 parts of sodium chloride and 80 to 20 parts of potassium chloride to which is added per 100 parts of said mixture, from about 1 to 20 parts of magnesium fluoride, said flux containing not more than about 5 per cent of magnesium chloride, whereby the surface of the article is first fiuxed and then brought into contact with the coating metal, holding the article in the molten coating metal so as to permit the same to displace the flux from and wet the surface of the article, and then withdrawing the wetted article from the molten body of coating metal through the flux layer, and cooling the withdrawn article in an inert atmosphere.

2. The method according to claim 1 in which the inert atmosphere is argon.

3. The method according to claim 1 in which the inert atmosphere is helium.

CLYDE A. MOE.

JOHN S. PEAKE.

GEORGE T. SERMON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. THE METHOD OF PRODUCING AN ADHERENT COATING OF A COATING METAL OF THE GROUP CONSISTING OF MAGNESIUM AND MAGNESIUM ALLOYS UPON ARTICLES OF FERROUS METAL WHICH COMPRISES INTRODUCING THE ARTICLE TO BE COATED INTO A MOLTEN BODY OF THE COATING METAL THROUGH A FLUX LAYER FLOATING UPON SAID MOLTEN BODY OF COATING METAL, THE FLUX CONSISTING OF A MIXTURE OF 20 TO 80 PARTS OF SODIUM CHLORIDE AND 80 TO 20 PARTS OF POTASSIUM CHLORIDE TO WHICH IS ADDED PER 100 PARTS OF SAID MIXTURE, FROM ABOUT 1 TO 20 PARTS OF MAGNESIUM FLUORIDE, SAID FLUX CONTAINING NOT MORE THAN ABOUT 5 PER CENT OF MAGNESIUM CHLORIDE, WHEREBY THE SURFACE OF THE ARTICLE IS FIRST FLUXED AND THEN BROUGHT INTO CONTACT WITH THE COATING METAL, HOLDING THE ARTICLE IN THE MOLTEN COATING METAL SO AS TO PERMIT THE SAME TO DISPLACE THE FLUX FROM AND WET THE SURFACE OF THE ARTICLE, AND THEN WITHDRAWING THE WETTED ARTICLE FROM THE MOLTEN BODY OF COATING METAL THROUGH THE FLUX LAYER, AND COOLING THE WITHDRAWN ARTICLE IN AN INERT ATMOSPHERE. 